The present invention is directed to water-inactivatable pressure-sensitive adhesives.
It is generally recognized that liquids are effective in reducing the adhesion to skin of pressure-sensitive adhesives, especially in the form as employed in adhesive medical devices. Liquids manifest their effect in several ways such as (1) interaction with the adhesive mass so as to alter the viscoelastic properties of the adhesive resulting in adhesive and/or cohesive failure, or (2) by disrupting the skin/adhesive contact interface. Rarely, although occasionally, the liquid acts upon the interface between the adhesive and any backing support employed. The extent and type of liquid interaction determines the ultimate performance of the adhesive product.
Those liquids which normally affect the performance of pressure-sensitive adhesive devices include body exudations, moisture from normal respiration of the skin, and externally-applied liquids such as water.
Coping with the effect of such liquids has been a primary concern of pressure sensitive adhesive suppliers. In general, it is recommended that an application site (such as the skin) be prepared by cleaning and drying immediately prior to application of the adhesive. For most short duration applications, such preparation is quite effective. However, in many situations, the adhesive device is required to remain adhesively secured to the skin for an extended period of time.
To ensure adequate functionality of the adhesive, suppliers have focused upon two avenues of approach. First, hydrophobic adhesives are employed which are substantially incompatible with those liquids with which they will come into contact. Such adhesives are also designed to be fairly aggressive by nature in terms of the degree of adhesion to the skin. Although effective in anchoring the medical device to the skin, the disruption of skin integrity resulting from attempts to remove the device from contact with the skin can be quite painful and/or irritating to the patient. This is particularly true in those areas where repeated applications to the skin are made, or where the skin is fragile. Any disruption to the integrity of the skin which results can be a significant disadvantage in terms of potential infection, as the protective effect of the skin is compromised.
By way of a second approach, liquid is removed from the skin/adhesive interface. This is accomplished by one of two methods. First, the adhesive device is designed so as to provide a water vapor transmission rate through the device which exceeds the normal respiration rate of the skin. This also assists in reducing masceration of the skin commonly experienced with adhesive medical devices. Such adhesive systems are disclosed in U.S. Pat. Nos. 3,645,835; 4,485,809; 4,452,845; and 4,561,435.
Secondly, a "hydroactive" adhesive composition is employed which is water absorbent. This tends to reduce the moisture content at the skin/adhesive interface, while also reducing the frequency of interfacial failure of the adhesive device.
Unfortunately, if the degree of moisture absorbance is excessive, cohesive failure of the adhesive can result. Tacky or sticky adhesive residue will possibly remain on the skin upon removal of the device, which must then be removed from the skin. Examples of such adhesives are disclosed in U.S. Pat. Nos. 3,339,546; 4,147,831; 4,350,785; 4,393,080; 4,505,976; 4,551,490; and 4,650,817.
It is thus desirable to provide a pressure-sensitive adhesive composition which exhibits an aggressive adhesive ability but which may be removed with ease from a substrate to which the adhesive is applied while minimizing the amount of residue which remains.